The present invention relates to a so-called projector type vehicle headlamp, and more particularly, the invention relates to a vehicle headlamp so configured as to form a low-beam luminous distribution pattern.
A projector type vehicle headlamp is normally equipped with a projection lens arranged on an optical axis extending in the longitudinal direction of a vehicle and a light source disposed behind the rear-side focal point, so that light from the light source is reflected by a reflector toward the optical axis.
In JP-U-02-047704, a so-called side-inserted type lighting device is described with reference to a projector type vehicle headlamp of the sort mentioned above, the lighting device being configured such that a light source bulb is fixedly inserted into a reflector from the lateral side of an optical axis.
The adoption of such a side-inserted type lighting device as described in JP-U-02-047704 makes it possible to render the lighting device compact by decreasing its longitudinal length.
However, as described in JP-U-02-047704, since many light source bulbs are formed to have line light sources extended in the axial direction of the bulbs, the following problems develop when the side-inserted type lighting device is employed.
More specifically, the light distribution of the line light source has such luminous intensity distribution that the luminous intensity is greatest in a direction perpendicular to the axis of the bulb and it is lowest in the axial direction of the bulb. Consequently, when the side-inserted type lighting device is employed, the problem is that as the quantity of light incident on an area in the forward direction in which the bulb is inserted on the reflective surface of the reflector becomes extremely small, it is difficult to secure sufficient brightness of the luminous distribution pattern formed by the light irradiated from the vehicle headlamp.
When the low-beam luminous distribution pattern is formed in particular, another problem is that as a predetermined cutoff line is formed by shading part of the light reflected from the reflector with a shade disposed in the vicinity of the rear-side focal point of a projection lens, formation of a bright luminous distribution pattern tends to become more difficult.